SCIENCE FILE

Arctic sea ice is approaching its lowest level in 30 years

Sea ice in the Arctic Ocean has reached its second lowest level in nearly 30 years, according to new satellite measurements released this week.

The National Snow and Ice Data Center reported that sea ice in the Arctic now covers about 2.03 million square miles. The lowest point since satellite measurements began in 1979 was 1.65 million square miles set last September.

With about three weeks left in the Arctic summer, this year could wind up breaking that record, according to scientists.

Arctic ice always melts in summer and refreezes in winter.

But over the years, more of the ice is lost to the sea with less recovered in winter.

While ice reflects the sun's heat, the open ocean absorbs more heat and the melting accelerates warming in other parts of the world.

"We could very well be in that quick slide downward in terms of passing a tipping point," said senior scientist Mark Serreze at the data center in Boulder, Colo. "It's tipping now. We're seeing it happen now."

NASA ice scientist Jay Zwally added that within "five to less than 10 years," the Arctic could be free of sea ice in the summer.

"It also means that climate warming is also coming larger and faster than the models are predicting, and nobody's really taken into account that change yet," he said.

The most recent ice retreat primarily reflects melt in the Chukchi Sea off Alaska's northwest coast and the East Siberian Sea off the coast of eastern Russia, according to the center.

The melt in sea ice has kicked in a long-predicted effect called "Arctic amplification," Serreze said.

That's when the warming up north is increased in a feedback mechanism and the effects spill southward starting in autumn, he said.

Over the last few years, the bigger melt has meant more warm water that releases more heat into the air during fall cooling, making the atmosphere warmer than normal.